Revert "bpf: add percpu stats for bpf_map elements insertions/deletions"

This reverts commit a6fb03a9 which is
commit 25954730 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: Idf75ac8d96a98127aac4ccf1d0c78dd4668f5664
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>